1. Field of the Invention
The invention is directed to an internal combustion engine with at least one combustion chamber for burning a fuel in timed explosions accompanied by formation of a combustion gas, wherein the combustion chamber is connected with at least one expansion chamber which is separate from the combustion chamber and which has a piston for converting energy of the combustion gas into mechanical energy or work. Further, the invention is directed to a method for operating an internal combustion engine of this type.
2. Description of the Related Art
An engine of the kind mentioned above is known from EP 957 250 A2. The advantage of an engine of this type with separate combustion chamber and expansion chamber is that the conditions for the combustion of the fuel and for the expansion of the combustion gas formed during combustion can be predetermined independently from one another, so that a high degree of efficiency can be achieved. A further improvement in efficiency compared with conventional two-stroke, four-stroke or diesel engines is achieved in this known engine in that, for each explosion stroke, the combustion chamber is filled with a constant, optimal charge of combustible mixture. To control the power output of the engine, the charging of the combustion chamber is not changed; rather, idle strokes are also inserted between working strokes in which the combustible mixture is ignited in the combustion chamber. There is no ignition of the mixture in these idle strokes; the mixture remains unburned in the combustion chamber. In order to make it possible to transmit the drive output of an engine controlled in this manner to a drive shaft, for example, of a wheel in a motor vehicle, relatively complicated steps are necessary in EP 957 250 A2. In an embodiment example, the piston of the expansion chamber is connected with a connecting rod which drives the drive shaft via an automatic transmission which is controlled in accordance with the required output and the required torque. In this regard, there is considerable expenditure on control and, moreover, lateral forces are exerted on the piston by the crankshaft, so that oil lubrication of the piston is required. In another embodiment example in EP 957 250 A2, the piston of the expansion chamber advantageously remains in an idle stroke at its top dead center. A hydraulic transmission device which, again, is relatively complicated is necessary for transmitting the drive output.
It is the primary object of the invention to enable simplified transmission of the output of the piston of the expansion chamber to a drive shaft in an internal combustion engine of the type mentioned in the beginning, wherein idle strokes or stroke pauses in which the piston of the expansion chamber remains in its top dead center can be inserted in addition to working strokes in order to control the engine (preferably with constant loading of the combustion chamber) such that efficiency is optimized. This highly complex problem is solved according to the invention in a surprisingly simple manner in that a drive shaft can be driven by the piston of the expansion chamber via a cam drive or cam gear unit having a cam disk and associated thrust member, wherein the thrust member can be lifted from the cam disk for implementing irregular engine cycles independent from a continuous rotation of the cam disk, including a pausing of the piston of the expansion chamber at its top dead center.
Cam gear units have a cam disk with a correspondingly shaped circumferential contour and (as driving or driven element) a thrust member contacting the cam disk. A cam gear unit of this kind enables a simple separation of the piston of the expansion chamber from the drive shaft during an idle stroke or stroke pause when a running face of a cam disk is provided for the thrust member only on one side and the thrust member remains raised from the cam disk during the idle stroke or stroke pause. The thrust member is advantageously formed by the free end of the piston rod which, for this purpose, is advantageously constructed as a roller tappet acting on a cam disk arranged at the drive shaft. The use of a cam disk also makes it possible to operate the internal combustion engine without oil lubrication for the piston (as will be explained in more detail).
For internal combustion engines which do not belong to the generic type because they do not have an expansion chamber that is separate from a combustion chamber but, rather, have a work piston that is arranged directly in the combustion chamber, the use of special cam gear units has already been suggested in particular, for example, in U.S. Pat. No. 5,813,372. However, this cam gear unit is used for other purposes and not to make it possible to add idle strokes between two explosion strokes; idle strokes of this type cannot be carried out at all in this kind of engine. Further, in these internal combustion engines, the thrust members of the cam gear units are positively guided because of the cam disks acting on both sides of the thrust members and it is not possible to raise the thrust member from the cam disk. Since a separate compression stroke must be carried out in these engines, this positive guiding of the thrust rod is required.
In a preferred embodiment example of the invention, a precompressor device which is separated from the combustion chamber is provided for precompression of air to be introduced into the combustion chamber. Using separate precompressor devices in this way in timed internal combustion engines is already known, for example, from DE 32 14 516 A1. In a particularly preferred embodiment example, the piston rod of the piston of the precompressor device is connected with the piston of the expansion chamber by a shared piston rod.
Further, at least one injection nozzle opening into the expansion chamber is advantageously provided for injecting a coolant liquid to introduce an implosion stroke following the explosion stroke. The energy inherent in the combustion gas can be better exploited by an implosion stroke of this kind so that a further increase in efficiency is achieved. The energy guided off in the implosion stroke is advantageously utilized for precompression by transmission to the precompressor device.
Further advantages and details of the invention are explained in the following with reference to an embodiment example of the invention shown in the drawing.